The present invention relates to valves having rotatable valve plates for throttling the flow of gas; more particularly, to throttle valves for internal combustion engines; and most particularly, to a throttle valve having a throttle shaft of about the same diameter as the valve throat and having a valve plate integral with the shaft.
Throttle-type valves for controlling the flow of gas are well-known. In the prior art, one type of conventional throttle valve typically comprises a body having a relatively is large-diameter first bore therethrough for passage of gas and a second relatively small-diameter bore transverse to the first bore for supporting a rotatable shaft on which is mounted a valve plate (known in the art as a xe2x80x9cbutterflyxe2x80x9d) for controllably occluding the first bore in response to rotation of the shaft to control the flow of gas. For clarity in the following presentation, such valves are referred to as prior art butterfly valves.
Several problems exist in conventional prior art butterfly throttle valves.
First, although the air bore, or throat, of the valve body is typically cylindrical, the valve plate is not circular but preferably is slightly elliptical such that the bore is sealed with the valve plate non-orthogonal to the axis of the bore. This is intended to prevent the plate from becoming jammed, or xe2x80x9ccorked,xe2x80x9d in the bore in the closed position. This problem can easily occur because the clearances between the valve plate and air bore in the closed position must necessarily be as small as is practically possible to minimize air leakage past the plate. Particularly in very small-displacement engines, the leakage inherent in prior art valves can be unacceptably large and irreducible without large expense in increased manufacturing control of component variability.
Second, because the valve plate is much larger in diameter than the diameter of the shaft bore, the plate cannot be formed integrally with the shaft but rather must be formed separately and mounted onto the shaft during assembly of the valve, typically by a pair of screws, after the shaft is installed into the valve body. Because of necessary tolerances in the manufacture of all components, significant and undesirable variation among valves occurs in the xe2x80x9cship airxe2x80x9d volume (referring to the inherent leakage through the closed valve) of the valves as shipped from the manufacturer.
Third, the geometric relationship of the valve plate to the valve bore in a prior art butterfly valve is inherently and geometrically poor for precise flow control of gas at very low opening angles, which unfortunately is where high precision is very desirable. As the valve plate begins to rotate away from the closed position against the valve body, the entire circumference of the plate loses contact with the bore wall simultaneously, and gas flows around the entire metering perimeter of the plate; thus, the flow of gas through the valve increases from the ship air volume very rapidly with rotation of the valve plate through very small angles from closed.
U.S. Pat. No. 5,678,594 discloses a second type of prior art throttle valve which overcomes the first two of these problems but not the third. As shown presently in FIGS. 1-3 (corresponding to the prior art FIGS. 2, 3 and 6, respectively), and discussed here for clarity of presentation of the prior art, a throttle valve 10 includes a valve body 12 defining a flow path extending from a cylindrical inlet 14 to a cylindrical outlet 16 having axes 15,17, respectively. The flow path is not smoothly cylindrical from inlet 14 to outlet 16 but rather is provided with transverse arcuate portions 18 (shown as xe2x80x9c90xe2x80x9d in the reference patent) purportedly to reduce the aerodynamic torque on the valve and thus reduce actuation load. Because the portions 18 lie on opposite sides of the upper and lower portions of the valve, respectively, as shown in FIG. 3, inlet 14 is axially offset from outlet 16.
Valve body 12 is configured to be mounted in a duct and has two opposed 103 coaxial circular portals 20, 22 defining a cylindrical bore 24 through valve body 12 transverse of axes 15,17 and forming opposed linear sealing lips 26 defining a longitudinal valve seat in body 12.
A cylindrical xe2x80x9cflow modulatorxe2x80x9d 28 includes a central rectangular valve plate 30, analogous to a prior art butterfly, extending from a first edge 32 to a second edge 34. Perpendicular to these edges, plate 30 is bounded by first and second disk flanges 36,38 of substantially the same outer diameter as the diameter of bore 24 and of the width between edges 32 and 34. Flow modulator 28 also includes a small-diameter shaft portion 40 which is captured in bearings (not shown) and used for conventional rotary actuation (not shown) of the flow modulator. Edges 32,34 seal linearly against the valve seat defined by lips 26 over the entire length of the edges and lips when the valve is closed, unlike a prior art butterfly valve which seals radially against a cylindrical bore.
The valve disclosed in U.S. Pat. No. 5,678,594 and just described suffers from the same geometric disadvantage as the conventional butterly valves described earlier, leading to inherently imprecise flow control of gas at very low opening angles. As shown in FIG. 3, as the valve plate 30 begins to rotate away from the closed position, the entire lengths of edges 32,34 lose contact with the lips 26 simultaneously, and gas begins flowing across the entire metering length of edges 32,34; thus, the flow of gas through the valve increases very rapidly with rotation of the valve plate through very small angles from closed.
Therefore, there is a strong need for an improved throttle valve wherein the flow of gas through the valve increases slowly with rotation of the valve shaft as the valve is opened.
It is a principal object of this invention to provide an improved throttle valve wherein the flow of gas through the valve increases slowly with rotation of the shaft as the valve is opened.
It is a further object of this invention to provide an improved throttle valve wherein the minimum air flow is substantially lower than that routinely achievable with prior art valves.
It is a still further object of the invention to provide an improved large-shaft throttle valve wherein the shaft is journalled in the valve body without requiring roller bearings.
It is a still further object of the invention to provide an improved throttle valve wherein the volume of idle air for each individual valve is independently adjustable after assembly such that all such valves may be adjusted to a standard ship air volume.
It is a still further object of the invention to provide an improved throttle valve requiring fewer components and therefore costing less to manufacture.
Briefly described, the present invention is directed to an improved rotary throttle valve. A valve body has a first cylindrical bore for flow of gas, such as air, therethrough between an inlet and an outlet. Orthogonal to the first cylindrical bore is a second cylindrical bore having substantially the same diameter as the first bore. A flow modulator rotatably disposed in the second bore has first and second cylindrical portions disposed respectively on opposite sides of the first bore and separated by a central plate having a width equal to the diameters of the first and second bores such that when the modulator is rotated to place the width of the plate transverse to the first bore, the edges of the plate are fully engaged with the wall of the second bore and the valve is closed. As the modulator is rotated from the closed position, the edges of the plate become progressively less engaged with the wall of the second bore, the edge of the open area following the juncture lines of the first and second bores, and the open area of the first bore increases accordingly.
Preferably, an adjustable air bleed valve is provided for calibrating a standard minimum air flow through the closed valve. A threaded axial bore in the flow modulator extends through one of the cylindrical portions into the metering plate and exits through the opposite surfaces of the plate to provide pinhole orifices on either side of the plate in the gas flow path. A screw or needle valve in the bore adjusts the volume of bleed air passing through the plate when the valve is closed.